Document FR-A-2 765 855 describes an inflatable boat of the type in question and which comprises:                two side buoyancy tubes;        a floor that is rigid at least transversely and that is interposed between said tubes:        a flexible bottom sheet that covers the underside of the rigid floor and that is secured in watertight manner to said tubes; and        a hull of approximately V-shaped cross-section disposed under the flexible bottom sheet, which hull comprises at least a central longitudinal strip in the shape of a V-shaped trough that is rigid, and that is made up of a plurality of longitudinal segments assembled together end-to-end, and secured together by releasable fixing means.        
With reference firstly to FIGS. 1 and 2 of the accompanying drawings (which are reproductions respectively of FIGS. 4 and 9 of Document FR 2 765 855), it is recalled briefly that the inflatable boat, given overall numerical reference 1, has respective floats in the form of inflatable tubes 2 on each of its sides. The two tubes can be joined at the bow to give an overall U-shape that is open at the stern of the boat. The two buoyancy tubes 2 are interconnected at the stern by a transom (not shown in FIGS. 1 and 2) and at their bottoms via a floor 3 that is rigid, at least transversely.
A flexible bottom sheet 16 extends under the rigid floor 3 and covers the underside of the rigid floor 3, being secured in watertight manner to the two buoyancy tubes 2 and to the aft end of the rigid floor or to the transom.
Under the flexible bottom sheet 16, a hull 4 is situated that is approximately V-shaped in cross-section. The hull 4 comprises at least a central longitudinal strip 6 in the form of a V-shaped trough which is rigid and which is made up of a plurality of longitudinal segments assembled together end-to-end, and secured together by releasable fixing means.
In the example shown in FIG. 1, the rigid strip 6 occupies only the central portion of the hull 4, and the two portions of the hull that are situated on either side of the rigid strip 6 are made up of flexible strips 7 made of a material of the same type as the material of the flexible bottom sheet 16. Releasable fixing means 8 (e.g. and advantageously a rod engaged in a groove) secure the flexible strips 7 detachably to the rigid central strip 6, while, via their outermost longitudinal edges, the flexible strips 7 are secured at 13 to the flexible bottom sheet 16, as shown in FIG. 1 (or even to the buoyancy tubes 2 in the examples of FIGS. 1 to 3 in Document FR 2 765 855).
In the specific example shown in FIG. 1, the rigid floor 3 has a particular make-up since it is made up of a plurality of panels 9 (e.g. from two panels to four panels depending on the length of the boat, and typically three panels for a medium-sized boat) which are rigid (e.g. made of metal, in particular of aluminum or of aluminum alloy). In addition, each floor panel 9 has edges raised at an angle such that said edges lie approximately in alignment with the sides of the underlying hull.
In the configuration shown in FIG. 1, the flexible strips 7 are secured to the flexible bottom sheet 16 approximately along the folds 13 of the raised edges of the floor panels 9. In other words, the flexible bottom sheet 16 is provided on its bottom face with longitudinal flaps 7 that can be secured to the rigid central strip 6.
In order to hold the resulting assembly under tension, a spacer 5, advantageously of the pneumatically inflatable type, is interposed between the assembly comprising the rigid floor 3 and the flexible, bottom sheet 16, and the rigid central strip 6, as shown in FIG. 1.
In another example shown in FIG. 2, the hull 4 is constituted entirely and only by the central rigid strip 6 which is removably secured directly to the flexible bottom sheet 16 by means 8 as mentioned above, approximately along the folds 13 of the raised edges of the floor panels 9. A boat configured in this way is simpler to manufacture (flexible flaps 9 omitted) and easier to assemble (the fixing rod, which is, in this example, secured to or integral with the flexible bottom sheet 16, is tensioned better and is easier to engage into the groove provided in the edge of the central strip 6).
Document FR 2 765 855 gives the overall provisions for such boats, but it does not give any specific technical solution as regards assembly and structure of the component segments of the rigid central strip 6 of the hull 4. However, the rigidity of the hull, and therefore the rigidity of the central strip 6, which constitutes the working portion of said hull, is essential for guaranteeing that the boat has the required qualities (stability, and course-holding).
In addition, it should be emphasized that the whole purpose of boats of this type is to be capable of being assembled and disassembled as easily as possible, or even, for certain users, of being assembled and disassembled as quickly as possible and in difficult conditions (e.g. in the dark).